What kind of wood should I use for a platform that holds 200 lbs

I am making a flat platform with 4 leveling feet that can hold a heavy duty blower which is around 200 lbs. The platform is 21.5" x 22.5" as shown in this image (let me know if there are better designs):

I thought about using 0.5" steel plate but with these dimensions, it will cost me $200+. That is why I decided wood would be a good option although I am not sure what type of wood to use. What I need is something strong, will dampen vibrations from the blower and costs less than $100 (the cheaper the better).

yep. @integral hit it: 3/4 ply of any sort (CDX is fine) with 2x4 is ample. i have built many utility platforms using this, and they can easily take 200 lbs, especially if you orient the 2x4s as @phinds suggested. for greatest stability, let's say you upgrade the blower, you may want a crosspiece or two, stud-wall-style, but that would be the last you ever concern yourself with it. this sort of structure is so strong that your concerns shift to other things, such as whether the feet, casters or whatever, are stable enough.

i would pre-drill your holes and then use lubricated deck screws (deckmate, for instance) for maximum ease in construction, and incredible holding power, in addition to easy disassembly.

you can fancy things up a bit if you like, making a lip on top with 1x1 or 2x2 all around, so your blower doesn't inadvertently slide off. or if it has bolt-downs, of course ignore the lip suggestion. if you feel there's any risk with the blower punching through plywood (unlikely, but if things got really wet, rotted and such, it could be an issue after many years), then you might enjoy the comfort of having painted or otherwise treated the mounting surface, and you could brace the corners.... at some point you have a platform that elephants could step on.